1. Field of the Invention
The present invention refers to a reactive hot-melt adhesive.
Traditionally hot-melt adhesives (hot melts) are thermoplastic materials, which are heated for processing in a pistol or in another device to a temperature of 90.degree.-200.degree. C., and then are applied as a liquid mass to the substrates to be bonded.
During cooling the mass solidifies and quickly forms a stable bond.
The quick solidification and the lack of water and solvents are advantages of these hot-melt adhesives, compared with other adhesive systems.
But the thermoplastic behavior of hot-melts is a drawback, because the mechanical, and therefore adhesive characteristics, are strongly dependent on temperature. At an elevated temperature the hot-melt resoftens, and at a lower temperatures they tend to develop brittleness, and therefore, they may only be used in a more or less narrow temperature range.
In the last few years reactive polyurethane hot-melt adhesives have been introduced into the market. They are characterized in that after cross-linkage they lose their thermoplastic behavior and have good mechanical characteristics over a broad temperature range. Cross-linkage of the reactive isocyanate groups can be achieved with water, especially humidity, or with a heat liberated hydrogen-active compound.
The known solvent free, moisture hardenable prepolymeric isocyanates are liquid to soft-waxlike at room temperature and because of their low green strength and long reaction time have only limited possibilities for use.
2. Description of the Prior Art
From the DE-PS 2 401 320 there is known isocyanate-containing hot-melt adhesives composed of:
a) 20 to 73 percent by weight of an urethane prepolymer having terminal isocyanate groups on both ends, PA1 b) 2 to 25 percent by weight of a thermoplastic polymer selected from the group consisting of ethylenevinylacetate-copolymers, ethylene-acrylic acid-copolymers, ethylene-acrylate copolymers, atactic polypropylene and linear polyethyleneterephthalate-polymers,and PA1 c) 25 to 55 percent by weight of a tackifying resin, such as colophonium derivatives or terpene phenol-copolymers. PA1 a) 20 to 90 percent by weight of a prepolymeric isocyanate, PA1 b) 0 to 75 percent by weight of a thermoplastic polyurethane, and PA1 c) 5 to 50 percent by weight of a low molecular weight synthetic resin selected from the group consisting of ketone resins, ketone-aldehyde-condensation resins and/or hydrogenation products of acetophenone-condensation resins. PA1 at least one thermoplastic material, preferably in an amount from 20 to 90 percent by weight, especially from 50 to 65 percent by weight, PA1 at least one binder on isocyanate basis, preferably in an amount from 5 to 40 percent by weight, especially from 15 to 30 percent by weight, and PA1 at least one thixotropic agent, preferably in an amount from 3 to 30 percent by weight, especially from 8 to 20 percent by weight, and in that the isocyanate content, with reference to the total hot-melt adhesive mixture, is in the range of from 0.01 to 10 percent by weight, preferably in the range of from 0.1 to 1 percent by weight, especially in the range from 0.3 to 0.7 percent by weight. PA1 the at least one plasticizer, preferably in an amount from 2 to 30 percent by weight, especially in an amount from 5 to 10 percent by weight, and/or PA1 the at least one filler, preferably in an amount from 5 to 50 percent by weight, especially in an amount from 8 to 15 percent by weight, and/or PA1 the at least one additive, preferably in an amount from 0.001 to 5 percent by weight, PA1 whereby said percentages are with reference to the total hot-melt adhesive mixture. PA1 plasticizers selected from the group, consisting of phthalates, such as dibutyl-, dioctyl-, dicyclohexyl-, diisooctyl-, diisodecyl-, dibenzyl- or butylbenzylphthalate, phosphates with up to 8 C-atoms in the alkyl group, such as trioctylphosphate; epoxy-containing plasticizers, toluenesulfonamides, chloroparaffines, adipic acid esters, castor oils, etc.; PA1 a) adhesion promoters, especially silane-containing compounds, which may additionally contain at least one reactive group, such as epoxy-, isocyanate-, amine groups or double bonds, PA1 b) dyes or pigments, PA1 c) polyurethane catalysts, such as lead and/or tin compounds, occasionally combined with the use of further polyurethane catalysts, especially of tertiary amine-containing catalysts, PA1 d) UV-absorbing agents or stabilizers, such as phenolic antioxidants, screening agents, PA1 e) surface active additives, such as emulsifying agents, PA1 f) flame retardants, and PA1 g) fungistatic and/or bacteriostatic active substances. PA1 a) aromatic diisocyanates, such as, e.g., 4,4'-diphenylmethanediisocyanate, 2,4-toluene-diisocyanate, naphthylene-1,5-diisocyanate, 1,3- and 1,4-phenylenediisocyanate, and/or PA1 b) aliphatic or cycloaliphatic diisocyanates, such as hexamethylene-diisocyanate, 1,12-dodecanediisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane 1,3- and -1,4-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatemethylcyclohexane, 2,4- and 2,6- hexahydrotoluene-diisocyanate, hexahydro-1,3- and -1,4-phenyldiisocyanate, perhydro-2,4'and -4,4'diphenylmethane-diisocyanate, and PA1 c) polyoles having a molecular weight range from 400 to 10,000, preferably from 1000 to 5000, such as e.g. linear or branched PA1 polybutadienes, PA1 polycarbonates, PA1 polycaprolactones, PA1 polycaprolactams, PA1 polyethers, e.g., polyethylene oxides, polypropylene oxides, polybutylene oxides, polystyrene oxides, polyepichlorohydrines, polytetrahydrofuranes, PA1 polyesters, e.g., any condensation products of multivalent alcohols (e.g. ethylene-glycol, propyleneglycol-1,2 and -1,3, butylene-glycol-l,4 and -2,3, hexanediol-1,6, octanediol-1,8, glycerin, trimethylolpropane, pentaerythrite, chinite, mannite and sorbite, methylglycoside, diethylene glycol, polyethylene glycols, dipropylene glycol, polypropylene glycols with multivalent carboxylic acids and/or carboxylic acid anhydrides and/or carboxylic esters), e.g., succinic acid, adipic acid, octanedioic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, trimellitic acid, phthalic acid anhydride, tetrahydrophthalic acid anhydride, tetrachlorophthalic acid anhydride, glutaric acid anhydride, maleic acid anhydride, fumaric acid, terephthalic acid-dimethylester and terephthalic acid-bis-glycol-ester, each having terminal, primary and/or secondary OH-groups, whereby the OH-functionality is preferably in the range of around 2, and/or PA1 d) short chain diols with terminal, primary and/or secondary OH-groups, such as, e.g., ethylene-glycol, bis-hexanediol-1,6,-propylene glycol, bis-hexapropylene glycol, diethyleneglycol, bis-hexaethylene-glycol. PA1 a) aromatic diisocyanates, such as, e.g., 4,4'-diphenylmethane-diisocyanate, 2,4-toluene-diisocyanate, naphthylene-1,5-diisocyanate, 1,3- and 1,4-phenylenediisocyanate, triphenylmethane-4,4',4"-triisocyanate, polyphenyl-polymethylenepolyisocyanates, and/or PA1 b) aliphatic or cycloaliphatic diisocyanates, such as, e.g., hexamethylene-diisocyanate, 1,2-dodecane-diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3- and -1,4diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatemethylcyclohexane, 2,4- and 2,6-hexahydrotoluene-diisocyanate, hexahydro-1,3- and -1,4-phenyldiisocyanate, perhydro-2,4'- and -4,4'-diphenylmethane-diisocyanate, and PA1 c) polyoles having a molecular weight range of from 400 to 10,000, preferably of from 1000 to 5000, such as, e.g., linear or branched PA1 polybutadienes, PA1 polycarbonates, PA1 polycaprolactones, PA1 polycaprolactams, PA1 polyethers, e.g., polyethylene oxides, polypropylene oxides, polybutylene oxides, polystyrene oxides, polyepichlorohydrines, polytetrahydrofuranes, PA1 polyesters, e.g., any condensation products of multivalent alcohols (e.g., ethylene-glycol, propyleneglycol-1,2 and -1,3, butylene-glycol-1,4 and -2,3, hexanediol-1,6, octanediol-1,8, glycerin, trimethylolpropane, pentaerythrite, chinite, mannite and sorbite, methylglycoside, diethylene glycol, polyethylene glycols, dipropylene glycol, polypropylene glycols) with multi-valent carboxylic acids and/or carboxylic acid anhydrides and/or carboxylic esters, (e.g., succinic acid, adipic acid, octanedioic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, trimellitic acid, phthalic acid anhydride, tetrahydrophthalic acid anhydride, tetrachlorophthalic acid anhydride, glutaric acid anhydride, maleic acid anhydride, fumaric acid, terephthalic acid-dimethylester and terephthalic acid-bis-glycol-ester) each having at least 2 terminal primary and/or secondary OH-groups, PA1 d) short chain diols with terminal, primary and/or secondary OH-groups, such as, e.g., ethylene-glycol, bis-hexanediol-1,6,-propylene glycol, bis-hexapropylene-glycol, diethyleneglycol, bis-hexaethylene-glycol, and/or PA1 e) cross-linking agents, such as, e.g., trimethylolpropane, glycerin, hexanetriol, triethanolamine, sorbite, mannite, sucrose, ethylene-amine, ethanolamine, hexamethyleneamine, pentaerythrite. PA1 any glass, especially glass plates for use in automotive vehicles, composite glass plates, front walls of glass, PA1 any metal, which may be varnished, metallized or otherwise coated and/or pretreated, e.g., bodies of automotive vehicles, PA1 any metal alloy, which may be varnished, metallized or otherwise coated and/or pretreated, e.g., bodies of automotive vehicles, PA1 any plastic, PA1 any construction material, especially stones, concrete, mortar, road pavings, and PA1 any wood.
But at certain mixing ratios, mixtures of these components tend to be incompatible, have unstable molten masses, and have insufficient resistance to continuous stress. Also, the storage stability of these components is sometimes insufficient.
In DE-OS 3 236 313 there is described reactive hot-melt adhesives which are compatible, are melt stable, are storage stable mixtures in the absence of moisture, have great initial adhesion and have high thermostability. These reactive hot-melt adhesives were developed for the bonding of thermoplastic and duroplastic plastics, foam plastics, varnished surfaces, wood, paper, leather, rubber, textiles, metals, etc., and they consist of a mixture of:
These reactive hot-melt adhesives with the above mentioned mixing possibilities are only limited non sag during coating (i.e., a coating thickness of more than 2 mm may not be guaranteed), are very tacky and string-like, and after cooling are viscous and have poor plastic moldability Therefore, they are limited to certain applications.